The state Public Utilities Commission raises the maximum total capacity for all rooftop solar systems in an electric bill-slashing program to about 5,200 megawatts from 2,400 megawatts.

SACRAMENTO — California is poised to more than double its targeted electricity output from rooftop solar panels.

The state Public Utilities Commission on Thursday tweaked its rules to authorize an increase in the number of residential, commercial and government buildings that can participate in a program that allows solar users to lower their electricity bills by getting credit for excess power sent back to the grid.

The move raises the maximum total capacity of all the state's rooftop solar systems to about 5,200 megawatts from a current 2,400 megawatts. That's enough new electricity to power about 2.1 million homes.

Proponents said the PUC's 5-0 decision would ensure that California would remain the nation's leader in solar power. The state's solar industry employs more than 25,000 workers and has raised more than $10 billion in private investment, they said.

"Solar energy provides a clean, renewable source of electricity for California homes and businesses," PUC President Michael Peevey said. "Today's decision ensures that the solar industry will continue to thrive for years to come, and we are fully committed to developing a long-term solution that secures the future of the industry in California."

The PUC boosted its so-called net metering program by making a technical change in the way it calculates how many electricity ratepayers can participate in the program. Putting more panels on homes and other buildings will save money, reduce dependence on fossil fuels and help meet an ambitious state requirement to generate at least a third of its power from solar, wind and other renewable sources by 2020, proponents said.

The move, though, was criticized by some consumer groups and utilities. They contend that expansion of the program would create an unfair subsidy to wealthier people who can afford to install solar arrays costing thousands of dollars. As a result, some of the net metering cost would be shifted to lower-income homeowners, renters and other people who don't want or need solar power, they said.

That argument is a matter of dispute. A 3-year-old PUC study pegged the subsidy at $140 million annually. A more recent look by a Berkeley energy consultant, R. Thomas Beach, concluded that the benefits to society, such as reducing carbon emissions to combat global warming, outweighed the subsidy costs.

As part of its latest ruling, the PUC authorized another cost-benefit analysis to be completed in October 2013 so that regulators could fine-tune the net metering incentive to solar owners. Peevey said he hoped that the analysis would be completed so the program could be reauthorized and avoid being automatically suspended Jan. 1, 2015.

The call for new studies persuaded one skeptical commissioner, Michael Florio, to support the solar net metering expansion. Florio, formerly an attorney for a San Francisco consumer advocacy group, the Utility Reform Network, said it's difficult to encourage renewable energy development while protecting the average ratepayer from high electric bills.

"Reasonable people on both sides of this issue now have to sit down and work out a long-term plan … that everyone can live with," he said.